Abstract
DNA methylation plays an important role in plant growth and development, gene expression regulation, and maintenance of genome stability. However, only little information regarding stress-related DNA methyltransferases (MTases) genes is available in tomato. Here, we report the analysis of nine tomato MTases, which were categorized into four known subfamilies. Structural analysis suggested their DNA methylase domains are highly conserved, whereas the N-terminals are divergent. Tissue-specific analysis of these MTase genes revealed that SlCMT2, SlCMT3, and SlDRM5 were expressed higher in young leaves, while SlMET1, SlCMT4, SlDRM7, and SlDRM8 were highly expressed in immature green fruit, and their expression declined continuously with further fruit development. In contrast, SlMETL was highly expressed in ripening fruit and displayed an up-regulated tendency during fruit development. In addition, the expression of SlMET1 in the ripening of mutant rin and Nr tomatoes is significantly higher compared to wild-type tomato, suggesting that SlMET1 was negatively regulated by the ethylene signal and ripening regulator MADS-RIN. Furthermore, expression analysis under abiotic stresses revealed that these MTase genes were stress-responsive and may function diversely in different stress conditions. Overall, our results provide valuable information for exploring the regulation of tomato fruit ripening and response to abiotic stress through DNA methylation.
Highlights
DNA methylation plays a crucial role in gene expression regulation, maintenance of genome stability, and it controls the transcription of invading and mobile DNA elements (Law and Jacobsen, 2010; Feng and Jacobsen, 2011)
Nine tomato MTases genes are dispersedly located on chromosomes, with one MTase variant mostly located on a single chromosome (Table 1), suggesting at least partial influence of WGD in the diversification of the MTases family in tomato, rather than gene duplication
Each of the tomato MTases genes has a homologous gene in Arabidopsis, suggesting that MTases in tomato might have similar roles as in Arabidopsis
Summary
DNA methylation plays a crucial role in gene expression regulation, maintenance of genome stability, and it controls the transcription of invading and mobile DNA elements (Law and Jacobsen, 2010; Feng and Jacobsen, 2011). Plants possess four types of DNA methyltransferases (MTases), namely methyltransferase (MET), chromomethylase (CMT), domains rearranged methyltransferase (DRM), and DNA methyltransferase homologue 2 (DNMT2) (Law and Jacobsen, 2010). DNMT2 has a novel transfer RNA (tRNA) methyltransferase activity (Goll et al, 2006; Jeltsch et al, 2006), but its role in C5 DNA methylation remains largely unknown (Pavlopoulou and Kossida, 2007). DNA methyltransferase plays an important role in plant development, transcriptional regulation, and metabolic pathway control. The Colorless non-ripening (Cnr) mutation inhibits normal tomato ripening due to methylation of the SBP-CNR gene promoter (Manning et al, 2006; Giovannoni, 2007). Chen et al (2015) recently reported on the role of a chromomethylase (SlCMT3) for the stable methylation of the promoter region of the Cnr gene
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